Resolving the Structure of Ionized Helium in the Intergalactic Medium with the Far Ultraviolet Spectroscopic Explorer

The neutral hydrogen (H I) and ionized helium (He II) absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000 to 1187 angstrom band at a resolv...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2001-08, Vol.293 (5532), p.1112-1116
Main Authors: Kriss, G. A., Shull, J. M., Oegerle, W., Zheng, W., Davidsen, A. F., Songaila, A., Tumlinson, J., Cowie, L. L., J.-M. Deharveng, Friedman, S. D., Giroux, M. L., Green, R. F., Hutchings, J. B., Jenkins, E. B., Kruk, J. W., Moos, H. W., Morton, D. C., Sembach, K. R., Tripp, T. M.
Format: Article
Language:English
Subjects:
Absorption and adsorption
Absorption spectra
Astronomy
Astrophysics
Characteristics and properties of external galaxies and extragalactic objects
Earth, ocean, space
Exact sciences and technology
Galaxies
Gas absorption
Gas adsorption
Gases
Helium
Hubble Space Telescope
Hydrogen
Intergalactic matter
quasar absorption and emission-line systems
lyman forest
Intergalactic medium
Light
Line spectra
Observations
Opacity
Quasars
Radiation
Red shift
Spectral index
Stars & galaxies
Stellar systems. Galactic and extragalactic objects and systems. The universe
Ultraviolet radiation
Wavelengths
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Summary:The neutral hydrogen (H I) and ionized helium (He II) absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000 to 1187 angstrom band at a resolving power of 15,000. We resolve the He II Lyman α (Lyα) absorption as a discrete forest of absorption lines in the redshift range 2.3 to 2.7. About 50 percent of these features have H I counterparts with column densities$N_{H\>I} > 10^{12.3}$per square centimeter that account for most of the observed opacity in He II Lyα. The He II to H I column density ratio ranges from 1 to >1000, with an average of ∼80. Ratios of 100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The presence of He II Lyα absorbers with no H I counterparts indicates that structure is present even in low-density regions, consistent with theoretical predictions of structure formation through gravitational instability.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1062693